The starting point of the present invention is an electric tool, especially an electric hand tool, according to the preamble of claim 1.
Electric hand tools always consist of a multitude of parts and components that have to be so arranged with respect to each other that--taken all together--they will constitute an operating assembly and have also to be so adjusted to each other as to ultimately yield an electrically driven tool that can be operated by the uninitiated and will possess both the required mechanical precision and the correspondingly necessary robustness.
In such tools an output shaft is driven, generally via a gear mechanism, by an electric motor that can in each case be activated by external switching means, the said output shaft, in its turn, then driving the tool associated with it, which may--for example--be a drill, a circular saw blade, a polishing disk, or the like. Traditional electric hand tools therefore consist in most cases of a two-shell housing, in which these parts are so fitted together that the housing itself, which generally consists of an appropriately hard plastic material (Duroplast), will not only serve as cladding or covering, but also acts as a structural or supporting element for the other components and will accommodate, in grooves or recesses for example, bearings for gear mechanisms or for the driving motor itself, so that the housing, at one and the same time, acts as a structural bearing element for the rotor and stator of the driving motor or the gear elements of the implement.
In a known hand tool machine of this type (DE-OS 34 13 233) a first bearing half shell for the rotor shaft end adjacent to the hand grip of the electric motor is connected to a housing half shell, and--with a view to the simultaneous grouping of the other bearing half shell with the first bearing half shell (pillow block)--a bearing bridge separate from the housing, which also acts as carrier of the electrotechnical components, is then so connected that the other housing half shell no longer has to perform any bearing or supporting function at all. In this way, even with the housing not yet closed, one obtains support for carbon brush holders, radio interference suppressors and any additionally provided luminescent indicators. The arrangement also makes it possible to check and test the implement while the housing is open.
It is also known (DE-OS 35 02 442) to arrange a motor bridge at one end of the stator of an electric motor, the design as a printed circuit of the said bridge being preferably such that it will support partial electric assemblies, including carbon parts, and that it will be connected to the stator both mechanically by means of fixing screws and electrically by means of appropriate contact tongues that ensure electric contact connection to the ends of the stator winding. This motor bridge also contains a seating opening for the associated roller bearing of the rotor shaft, so that mechanical prefixing to the stator also ensures appropriate alignment of the rotor with respect to the stator and the position of the air gap.
It is further known that the construction of such electric hand tools, hand drills being a case in point, can be simplified by basing the design, at least as far as the electric circuitry is concerned, on the use of electric plug-in components, so that the required electric wiring becomes reduced and a large number of current-conducting parts, including those for reversing the direction of rotation of the tool and switching it on and off, assumes the form of links that can be inserted in appropriate plastic components, including the housing itself, or in some cases be incorporated in these components already during their manufacture. One known electric hand tool (DE-OS 36 06 926) thus comprises a housing, the electric motor driving the implement and, as far as the electric circuitry is concerned, elements and leads in the form of block components that can be plugged into each other.
In connection with electric hand tools it is also known quite generally (DE-PS 33 11 557) that a bridge-like holding device--which can also be described as a motor bridge--can be arranged at one end of the stator of the electric motor for a hand tool. This motor bridge is intended to ensure the positioning and supporting of the rotor-shaft roller bearing that is held in this manner and can be appropriately connected to the stator--for example--by arranging pins on the end face of the motor bridge that point in the direction of the stator, the said pins making it possible to plug the motor bridge into the stator and thereby obtain correct alignment. In this way, relying on an appropriate seating aperture in the motor bridge to hold the associated roller bearing of the rotor shaft, one also obtains the final position that determines the air gap. But the real aim of this known method of supporting the rotor of an electric motor is really that of making it possible to balance the rotor together with the roller bearing fixed to the rotor shaft prior to assembly, i.e. to perform the balancing of the rotor with all the essential parts, including the rotor shaft roller bearing, and only afterwards insert the outer ring of the roller bearing into the appropriate recess in the motor bridge.
Notwithstanding such piecemeal simplifications in structure and form, known electric hand tools are still subject to the problem that the individual components constituting the implement are always interdependent to a greater or lesser extent, so that the accuracy of the two-shell housing will also--at least--codetermine the accuracy with which the electric driving motor is positioned and supported, a situation in which there may well arise advantages as regards the number of building components required for an individual assembly, while the final assembly and the checking of the proper functioning of the individual components and their interaction becomes all the more complicated. Consequently, and this represents an insight of the present invention, this development direction of manifold interdependencies between the individual building elements may reveal itself as a mistake that will make possible simplifications in the structure, form and design of electric hand tools up to a certain threshold value, but will thereafter have the opposite effect and bring in its wake greater costs as regards assembly, accuracy requirements to be met by individual components, testing for proper functioning, etc., and right through to the maintenance and--of course--also the repair of such tools.
It is, therefore, the object of the present invention to produce a fundamental change in the structural design of electric tools, especially electric hand tools, and at one and the same time to bring about a drastic simplification of this design and thus to ensure a substantially simpler final assembly of the implement, i.e. to introduce an improvement at a stage that hitherto invariably proved to be particularly costly and not capable of further automation, the said stage also comprising the final operational checkout.